The content of heavy metals in different areas of the shymkent city

At present, the problem of soil contamination with toxic compounds, including heavy metals, is becoming increasingly important. Heavy metals (HM) already now occupy the first place in terms of the degree of danger, and far ahead of such widely known pollutants. In the future, they can become more dangerous than waste from nuclear power plants and solid waste. Contamination of TM is associated with their widespread use in industrial production.

Soils can be polluted by the accumulation of heavy metals and metalloids due to emissions from rapidly developing industrial zones, tailing dumps, removal of heavy metal waste, leaded gasoline and paints, fertilizer, manure, sewage sludge, pesticides, sewage water, coal combustion residues, oil spills and atmospheric deposition [1, 2].

Metallurgical enterprises annually emit over 150 thousand tons of copper, 120 thousand tons of zinc, about 90 thousand tons of lead, 12 thousand tons of nickel, 1,5 thousand tons of molybdenum, about 800 tons of cobalt and about 30 tons of mercury . For 1 gram of blister copper, the copper smelting industry's waste contains 2.09 tons of dust, which contains up to 15% of copper, 60% of iron oxide and 4% of arsenic, mercury, zinc and lead. The wastes of engineering and chemical industries contain up to 1 thousand mg / kg of lead, up to 3 thousand mg / kg of copper, up to 10 thousand mg / kg of chromium and iron, up to 100 g / kg of phosphorus and up to 10 g / kg of manganese and nickel. Other materials are generated by various industries, such as textiles, tanning, petrochemicals due to accidental oil spills or the use of oil-based products, pesticides and pharmaceuticals and are highly variable in composition. Although some are disposed of on land, few have advantages for agriculture or forestry. In addition, many of them are potentially dangerous because of their heavy metals (Cr, Pb and Zn) or toxic organic compounds and are rarely ever applied to the earth. Others are very low in plant nutrients or do not have soil conditioning properties [3].

Fertilizers: Historically, agriculture was the first major human influence on the soil. To grow and complete the life cycle, plants must acquire not only macronutrients (N, P, K, S, Ca and Mg), but also the necessary trace elements. Some soils lack the heavy metals (such as Co, Cu, Fe, Mn, Mo, Ni and Zn) that are necessary for healthy plant growth, and yields can be supplied with them as a supplement to the soil or as foliar spray. Cereals grown on Cu-deficient soils are sometimes treated with Cu as an additive to the soil, and Mn can similarly be supplied to cereals and root crops. A large number of fertilizers are regularly added to soils in intensive agricultural systems to provide adequate N, P and K for crop growth. The compounds used to supply these elements contain trace amounts of heavy metals (for example, Cd and Pb) as impurities, which after prolonged fertilization can significantly increase their content in the soil. Metals, such as Cd and Pb, do not have a known physiological activity.

The overall objective of any soil remediation approach is to create a final solution that is protective of human health and the environment [4]. Remediation is generally subject to an array of regulatory requirements and can also be based on assessments of human health and ecological risks where no legislated standards exist or where standards are advisory. The regulatory authorities will normally accept remediation strategies that centre on reducing metal bioavailability only if reduced bioavailability is equated with reduced risk, and if the bioavailability reductions are demonstrated to be long term.

Chemical analysis to determine the content of gross forms of lead, copper, zinc and cadmium both in soil and in plant samples was carried out by the atomic-adsorption method in a special laboratory.

In each flower culture, the presence of a "biochemical barrier" at the boundary "underground (root) phytomass - aboveground phytomass" was determined and the biological absorption coefficient Ax of heavy metals was calculated according to the formula proposed.

Where - the content of heavy metals in ornamental plants; Kn is the content of heavy metals in the soil.

The content of cadmium in all soil samples was higher than the background level in 5 times more. The content of other heavy metals in different functional zones of the city (Table 1).

Table 1 – The content of heavy metals in different areas of the Shymkent city

So, in soil samples selected in the area of the main industrial zone of the city of Shymkent, the maximum of all samples of lead and zinc content exceeded the regional background value in 4.05 times and 2.4 times more respectively. Along the main transport routes, soil samples also contain a high amount of these metals, but the excess of background values is lower than in the industrial zone: lead by 12.1%, zinc by 25.7%. This fact is due to the fact that along the main transport highways in recent years, there is often a replacement of the upper urban soil. The contaminated upper soil layer is filled up with a new one, which does not contain contaminants, or it is completely removed. In the industrial and residential areas of the city, these events are not held. In the industrial soil deposits pollutants from the air for decades. In addition, the influence of private vehicles on the ecological state of soils also occurs within residential areas. It is for this reason that there is a high content of lead and zinc, both in industrial and residential areas, and also in the transport area – crossing Republic prospect and Tauke Han Avenue.

References

1. S. Khan, Q. Cao, Y. M. Zheng, Y. Z. Huang, and Y. G. Zhu, “Health risks of heavy metals in contaminated soils and food crops irrigated with wastewater in Beijing, China,” Environmental Pollution, vol. 152, no. 3, pp. 686–692, 2008.
2. M. K. Zhang, Z. Y. Liu, and H. Wang, “Use of single extraction methods to predict bioavailability of heavy metals in polluted soils to rice,” Communications in Soil Science and Plant Analysis, vol. 41, no. 7, pp. 820–831, 2010.
3. T. Basta, J. A. Ryan, and R. L. Chaney, “Trace element chemistry in residual-treated soil: key concepts and metal bioavailability,” Journal of Environmental Quality, vol. 34, no. 1, pp. 49–63, 2005.
4. Scragg, Environmental Biotechnology, Oxford University Press, Oxford, UK, 2nd edition, 2006.